Amazon's move is meant "to help out with analytics and data-crunching applications," said Redmonk analyst Michael Coté. "While databases, middleware, and other algorithms have gotten around memory limitations for years, simply having more memory to work with is an effective way to brute-force much computation."

While many AWS customers purchase processing capacity on a pay-as-you-go basis, reserved instances let them make a one-time payment to secure an instance for a fixed term. In exchange, the customer gets a discount on hourly charges.

Amazon already offers Windows for on-demand instances.

"The issue, as with all metered execution in the cloud, is making sure the applications run the minimal amount of time, thus, are cheaper to run than dedicated servers," Coté said.